DESCRIPTION: The goal of this application is to determine the turnover rate o actin within hair cell stereocilia. This will be accomplished using a prototy secondary ion mass spectroscopy (SIMS) microscope to image cochlear preparatio from mice fed the stable nitrogen isotope, nitrogen-15. By examining, with hi spatial resolution, the appearance and disappearance of incorporated nitrogen-into stereocilia, these investigators hope to estimate the rate at which stereociliary actin molecules are continually turned-over in the normal cochle Such data, they suggest, will be important in understanding molecular aspects some forms of hearing impairment as well as introducing a potentially powerful new technique with many applications in inner ear research.